PHP实现从远程下载文件的方法

<?php
if ($_GET[xfer]) {
if ($_POST[from] == "") {
print "You forgot to enter a url.";
} else {
copy("$_POST[from]", "$_POST[to]");
$size = round((filesize($_POST[to])/1000000), 3);
print "transfer complete.<br>
<a><a href="$_POST[from]">$_POST[from]</a><br>
<a><a href="$_POST[to]">$_POST[to]</a> : $size MB";
}
} else {
print "<form action="$PHP_SELF?xfer=true" method=post>
from(http://): <input name=from><br>
to(filename): <input name=to><br>
<input type=submit value="transload">";
}
?>